text: At low temperatures, some metals can undergo a ductile-brittle transition which makes the material brittle and could lead to catastrophic failure during operation. This temperature is commonly called a ductile-brittle transition temperature or embrittlement temperature. Research has shown that low temperature embrittlement and brittle fracture only occurs under these specific criteria:
  # There is enough stress to nucleate a crack.
  # The stress at the crack exceeds a critical value that will open up the crack (also known as Griffith's criterion for crack opening).
  # High resistance to dislocation movement.
  # There should be a small amount of viscous drag of dislocation to ensure opening of crack.
  All metals can fulfill criteria 1, 2, 4. However, only BCC and some HCP metals meets the third condition as they have high Peierls barrier and strong energy of elastic interaction of dislocation and defects. All FCC and most HCP metals have low Peierls barrier and weak elastic interaction energy. Plastics and rubbers also exhibit the same transition at low temperatures.
  Historically, there are multiple instances where people are operating equipment at cold temperatures that led to unexpected, but also catastrophic, failure. In Cleveland in 1944, a cylindrical steel tank containing liquefied natural gas ruptured because of its low ductility at the operating temperature. Another famous example was the unexpected fracture of 160 World War II liberty ships during winter months. The crack was formed at the middle of the ships and propagated through, breaking the ships in half quite literally.